In U.S. Pat. No. 4,278,756, Bouldin et al. teach a reflective laser recording and data storage medium formed from a photosensitive silver-halide emulsion. The emulsion is exposed and developed using a negative silver diffusion transfer process to make the film surface shiny compared to data spots which are clear or dark. The shiny surface may be above or below the main body of the emulsion depending on whether the reading light is to be introduced from above or from below through a clear substrate. Data may be laser recorded, the laser light damaging the shiny film surface to create spots.
U.S. Pat. Nos. 4,360,728 and 4,503,135 to Drexler disclose a laser apparatus for recording and reading data on strips of direct-read-after-write optical storage media disposed respectively on a card and a photographic film sheet. The apparatus includes a laser light source emitting a beam that passes through collimating and focusing optics and onto a pair of servo controlled scanning mirrors. A card or sheet holder moves the strip lengthwise relative to the beam with course control, while one of the servo mirrors is for fine control of relative lengthwise motion. The other servo mirror moves the beam laterally onto another data track. Differences in reflectivity between data spots and the surrounding strip material are detectable by a light detector receiving light from the media via a beam splitter and focusing lens.
In reflective optical data storage media, high optical contrast between data spots and the media background and sharply defined data spots are necessary for resolving data, particularly where data spots are small, i.e. ten microns or less in size. For optical tape it is also desirable that the optical storage and recording media provide two capabilities in addition to high contrast and high resolution. The media should record with a laser beam, and it should be capable of pre-recording servo track guides or timing marks during manufacturing for those applications where such guides or timing marks are required. Optical tape is valuable with data bits as large as one to five microns while optical disks require data bits one micron or smaller to be valuable.
An object of this invention was to provide a system for laser recording of data on optical tape with high contrast and high resolution of the recorded data spots.